CODEWITHSUNDEEP
androidmemory-managementandroid-lru-cache
A Random Android Dev
A Random Android Dev

Reputation: 2691

Is it a good idea to store LRUCache object in an Application singleton?

I have an LRUCache that I use to cache thumbnails and other such small bitmaps. Currently, I'm using it in my main activity, however, I'd like to use it my other activities too. This makes me wonder if it's a good idea to simply store this LRUCache object in my custom application singleton (which extends Application) and solve the problem of accessing the cache in other activities. The reason why I'm concerned is because, as I understand it, if the application process is killed - which is very likely to happen when the app is left running for too long in background - the application object and therefore the cache will get garbage collected. Correct me if I'm wrong on that and help me understand this issue better/provide a solution to this problem.

Upvotes: 1

Views: 1977

Answers (2)

Ryhan
Ryhan

Reputation: 1885

My usual rule of thumb is, for persisted data use disk cache & for quick, dirty & light data, use memory cache (or your lru cache). Be careful with storing bitmaps in memory cache, at least for android devices < 2.3.3, I believe. The pixel data of the bitmap is actually stored in native memory so developers have less control to encourage garbage collections for it. For example, even setting your bitmap to null or invoking the recycle() method may not fully convince the garbage collector to free the bitmap in the dalvik heap (vm heap) since its a small object on the dalvik heap (vm heap), even though it's native counterpart in native memory is large cause OutOfMemoryException.

Sorry for straying off a bit but thought you should know. As for your the answer, your assumption is right. When android is running low on memory it retains the last user activity instance in it's system memory but may kill your process, where your process hosts your application object. So in your case, if you stored 5 bitmap objects in your application object, and users left for sometime, they may come back to an activity requesting a bitmap from a newly created application object by the system, which would then produce a null bitmap.

Given these circumstances the solution is typically clear. If you want to persist data, you can't trust object memory (in-memory, RAM), at least on Android, so disk memory might be your best option.

Hope this helps.

Upvotes: 1

Karakuri
Karakuri

Reputation: 38595

I think this is a perfectly fine idea. Here's a video from Google I/O 2012 with some relevant information: http://www.youtube.com/watch?v=gbQb1PVjfqM

Upvotes: 0

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